There is a need for improved devices and methods to treat several medical conditions. Several conditions including atrial fibrillation, cancer, Menorrhagia, wrinkles, etc. may be treated by ablating tissue by applying an ablating energy. Even though devices and methods exist to treat these conditions by ablating tissue, there is still an unmet need for improved devices and methods.
For example, microwave antennas (e.g. helical antennas) have been used in medical applications including treatment of benign prostate hyperplasia, cancer treatment, etc. Many of the existing antennas have common disadvantages such as device shaft heating and non-uniform lesion profile along the length of the antenna. Thus there is a need for microwave antennas that are capable of generating uniquely shaped microwave fields that overcome these problems. Several prior art antennas also need cooling mechanisms and sophisticated temperature monitoring systems to achieve acceptable clinical results.
Menorrhagia is one of the most common gynecological conditions in pre-menopausal women. It is characterized by excessive menstrual blood loss. The condition severely affects the quality of life of the affected women since it may interfere with physical activity, work and sexual activity. Several techniques have been developed that aim to destroy the uterine endometrium to treat menorrhagia in a minimally invasive manner. Such endometrial ablation techniques can be performed by a variety of methods such as radiofrequency heating, circulating hot saline in the uterine cavity, microwave heating, cryodestruction, laser destruction, etc. Every current endometrial ablation technique has some fundamental limitations. For example, the Hydrothermablator™ device by Boston Scientific needs a hysteroscope which adds to the procedure cost and complexity. Further the device is thick and rigid. Because of that, the procedure requires significant anesthesia, usually in the form of conscious sedation or general anesthesia. The Novasure™ device is also thick and rigid. Thus a significant amount of cervical dilation is needed to introduce the device into the uterine cavity. Since cervical dilation is very painful, the procedure requires significant anesthesia, usually in the form of conscious sedation or general anesthesia. Also, the device is expensive (˜$900). Thus, even though there are a variety of endometrial ablation devices, there is still a need for a small-size, flexible, low-cost, easy to use next-generation device in this large and growing market.
Several ablation modalities such as microwave ablation can be used to treat solid tumors (e.g. liver tumors) by heating up the tumor tissue. Devices that use microwave ablation for treating tumors are advantageous over devices that use other ablation modalities because of their potential to create larger, uniform volumetric lesions. In prior art microwave ablation devices, microwave energy is emitted by an antenna and transmitted to the tumor tissue. The efficacy of the ablation procedure depends significantly on the power efficiency and the SAR and thermal profile of the antenna. Most existing microwave ablation devices are derived from the simple monopole antenna and have a linear structure. Their SAR and thermal profile are substantially elliptical and they are approximately similar to the shape of a football as shown in FIG. 2E. It is difficult to use a single monopole antenna to ablate tumors that have a thickness or diameter of a few centimeters in a sufficiently short time. For many cancer-related applications, the targeted tumors have an excessive size (e.g. diameter of several centimeters) and a single monopole antenna is of limited use. One of the solutions proposed to increase the lesion size involves using multiple ablation devices simultaneously. This increases the complexity of the ablation system. The overall size and cost of the ablation device will also be increased due to more number of elements employed in the system. Also, this increases the invasiveness and complexity of the procedure.
Further, the SAR profile shown in FIG. 2F demonstrates that there is a significant amount of microwave field proximal to the distal end of the coaxial cable feeding the radiating element (monopole antenna). Thus the ablation will not be accurately contained in the region around the radiating element. A portion of the tissue surrounding the distal region of the coaxial cable will be ablated. This in turn carries a risk of damaging healthy tissue by the microwave energy. Thus there is a need for improved microwave ablation devices that are low profile and that can ablate a tissue volume without damaging adjacent healthy tissue.
Atrial fibrillation (AF) is a cardiac electrophysiological disorder found in millions of Americans. Various ablation systems, including catheters and surgical tools, are used to ablate cardiac tissue to treat atrial fibrillation. In catheter ablation procedures, several individual lesions are then created as part of a desired lesion pattern. In many existing procedures, only a single, small, point lesion is created at any given time. Multiple such point lesions are needed to achieve the desired clinical response in the patient. In such procedures, an electrophysiologist guides the ablation tip of an ablation catheter to a point on the left atrium and creates a first point ablation. Once the first point ablation is created, the electrophysiologist then guides the ablation tip to a new location on the left atrium and creates a second point ablation, typically in communication with the first point lesion. This process continues until the desired lesion pattern is created. The creation of such multiple, connecting point lesions is very time consuming and technically challenging. There are other limitations to point ablation systems. For example, during the translation of the ablation tip to a new location, the distal ablation tip may slip, or otherwise move across the target tissue in an undesired manner. The steps of translation of the ablation tip to a new location are further complicated by the motion of the left atrium because of the natural beating of the heart. Further, users of point ablation systems typically use costly support equipment to provide historic and current position information of the ablating portion with respect to anatomical cardiac structures and previously created lesions. The support equipment is extremely costly and requires additional personnel to operate, ultimately increasing procedure costs. Still another problem with point ablation devices having ablating tip portions is the risk of perforation. The forces applied to the ablation devices are transmitted by the relatively narrow ablation tip to the atrial wall. Thus the relatively narrow ablation tip exerts a significant amount of pressure on the atrial wall. This in turn may result in perforation of the atrial wall which in turn may lead to formation of a potentially fatal atrio-esophageal fistula. Thus, there is a need for improved ablation devices that simplify the procedure of catheter ablation for treating atrial fibrillation and have a low risk of complications.
In order to overcome the limitations of point ablation systems, devices comprising an array of multiple radiofrequency (RF) electrodes were developed. However, RF electrodes need excellent tissue contact throughout the length of the electrode(s). This is difficult to achieve using the prior art delivery systems leading to inconsistent contact between the RF electrode(s) and the target tissue. Such inconsistent electrode contact causes variability in the transmission of energy throughout the target length of ablated coagulated tissue. This inconsistency also produces undesirable gaps of viable tissue that promote propagation of wavelets that sustain atrial fibrillation, or produce atrial flutter, atrial tachycardia, or other arrhythmia substrate. Thus, there is a need for devices that create sufficiently deep lesions even without achieving perfect contact with the target tissue.
Thus, even though several methods and devices exist that treat clinical conditions by energy delivery, there are still unmet needs for improved methods and devices.